“The earth has one moon, and Mars has two. The smallest one is about six miles in diameter. It is the smallest heavenly body with which we are acquainted. The nearest of Mars’ moons is less than 4,000 miles from the surface of Mars. The nearness of this moon to Mars I would like to have you keep in mind, for my presence on earth is indirectly connected with this phenomenon, which I will soon tell you. “We must bear in mind that one year on Mars is nearly two years on earth. A person living eighty years on Mars lives about double the number of hours that a person who lives eighty years on earth does. “According to your ‘nebular hypothesis,’ which is true according to our astronomical knowledge Mars was detached from the sun ages before the earth was born; for Mars is farther from the sun--is located outside of the earth’s orbit. Mars is also much smaller and less dense than the earth, in consequence of which it cooled much longer and much more rapidly. Mars, then, is much older astronomically and geologically. The crust of Mars, in proportion to its diameter, is much thicker than the crust of the earth. The water area, in proportion to the land area, is much smaller on Mars than it is on earth, because the water is continually being absorbed by the thickening solid crust. We can readily see, then, that according to these data, other things being equal, Mars must have an older and more advanced vegetable and animal life. The Marsian social and industrial organizations must be much more perfect than yours. “On account of the difficult dynamical (pertaining to strength or power) principles involved in my interplanetary navigation, I shall for the present defer an explanation of my journey. It will, however, I think, not be out of place here to suggest that the force of gravitation between two bodies is in proportion to their mass and inversely as the square of their distance. The earth and Mars, when nearest together, are about 34,000,000 miles apart. There is a point, then, somewhere between them, where a body would be equally attracted by both, would neither fall to the earth nor to Mars. But, if moved a little toward either one, from the point of equilibrium, it would fall the whole distance toward that body with continuously increasing velocity. If the earth and Mars, when in conjunction, were only a mile apart, a body could easily, even with your present knowledge of dynamics, be projected out of the reach of gravitation of one of these planets into that of the other. The actual interplanetary distance, which I traversed between the earth and Mars, calls in nothing new in _kind_, but only in _degree_. So you see that in order to be able to make this interplanetary journey, you need only to _improve_ on what you already have; and time has given the inhabitants of Mars, on this point, the advantage over the inhabitants of the earth.” CHAPTER II. MIDITH’S ARRIVAL--HIS IDEAS OF OUR EARTH.